The spread spectrum CDMA communication system is popular in the recent years, wherein the RAKE receiver is proven to be the optimum choice for dealing with an external multipath signal in the CDMA communication system. FIG. 1 is a schematic diagram of a rake receiver 10 according to the prior art. The RAKE receiver 10 according to the prior art comprises a searcher 14, a plurality of RAKE finger tracking units 12a, 12b, 12c, a RAKE finger management 16 and a maximum ratio combiner 18. The three tracking units 12a, 12b, 12c, are utilized to simplify this case, however, more units can be accommodated.
When the RAKE receiver 10 receives an external multipath signal 13 from the antenna 11, the searcher 14 acquires the corresponding searching time position of the plurality of path signals 15, 17, 19 in the multipath signal 13 with a first predetermined resolution wherein the first predetermined revolution is 0.5 chip time. The objective of the searcher 14 is to identify the existence of the path signals 15, 17, 19, so we don't need a very exact resolution. If the first predetermined resolution were determined too precise, it would result in a huge rake receiver 10 and higher power consumption. The searcher 14 and the rake finger tracking units 12 need to match up with each other for the purpose of a small rake receiver, lower power consumption and exactly acquiring the time positions of path signals 15, 17, 19. Three of the plurality of the path signals are utilized to simplify this case, however, more units can be accommodated.
Every RAKE finger tracking units 12a, 12b, 12c aims to acquire the exact locations corresponding to the path signals, and each tracks a single path signal. Therefore, each of the RAKE finger tracking unit 12 depends on a predetermined tracking time position to track the location of the path signal around the predetermined tracking time position with a second resolution wherein the second revolution is higher than the first revolution, for example, 0.125 chip time. Then, the RAKE finger tracking units 12 acquire the tracking time positions of the path signals. The tracking time positions of the path signals are more precise than the searching time positions.
At last, all RAKE finger tracking units 12a, 12b, 12c combine the corresponding path signals 15, 17, 19 via a maximum ratio combiner (MRC) 18 to obtain the corresponding signal S2 of the multipath signal 13. The signal S2 comprises the largest signal-noise ratio after the aforementioned steps.
Due to the variation of the multipath signals, the predetermined tracking time position is not always suitable for the path signals 15, 17, 19, or several predetermined tracking time positions correspond to the same path signal. This means that there is any idle rake finger tracking units or several rake finger tracking units are tracking the same path signal which causes the waste and idle units in the rake receiver.
Thus, besides the three major parts, the RAKE finger management (RFM) 16 plays an important role in the RAKE receiver. The subject of the RAKE finger management 16 is to assign and manage the RAKE finger tracking units 12a, 12b, and 12c. The RAKE receiver receives the plurality of multipath signals with the limited RAKE finger tracking units. The problem needing to be solved is to bring the RAKE receiver into full play with limited resources.